Wear OS watches [or for that fact, even Apple ones] aren't very great on battery life. Samsung Galaxy 6/Pixel Watch 2 can eke out couple of days if used with AOD turned off. But start doing things like streaming music from watch to earbuds and battery takes a tumble.
I used a fitness tracker before. In hindsight, it wasn't as accurate as even the couple of years old Galaxy Watch 4, but it had couple of weeks of battery life.
A fun fact, there's a local company here that actually installed full blown Android and in their marketing jargon, created a "wristphone". Problem is, they are marketing it to people who wish to consume videos and stuff on watches [ why would anyone want to do that, I dunno] but it's battery life, as expected, doesn't inch beyond 2 hours.